Adapt a custom device or firmware reader

Format crates consume hadris-io traits rather than requiring std::io. Hosted std::io readers work directly. Embedded devices implementing embedded-io can be wrapped without erasing their source error.

[dependencies]
embedded-io = "0.7"
hadris-fat = {
  version = "2.1.0",
  default-features = false,
  features = ["read", "sync"]
}
hadris-io = { version = "2.1.0", default-features = false, features = ["sync"] }

use embedded_io::{ErrorType, Read, Seek, SeekFrom};

struct FirmwareDisk {
    // Firmware protocol handle and current position.
}

impl ErrorType for FirmwareDisk {
    type Error = DeviceError;
}

impl Read for FirmwareDisk {
    fn read(&mut self, buf: &mut [u8]) -> Result<usize, Self::Error> {
        // Read from the firmware or device protocol into `buf`.
        todo!()
    }
}

impl Seek for FirmwareDisk {
    fn seek(&mut self, position: SeekFrom) -> Result<u64, Self::Error> {
        // Validate the requested position and update the device cursor.
        todo!()
    }
}

let disk = FirmwareDisk { /* ... */ };
let reader = hadris_io::sync::FromEmbedded::new(disk);
let volume = hadris_fat::sync::FatVolume::open(reader)?;
# Ok::<(), hadris_fat::Error>(())

The device must provide the access pattern required by the format. Mounted filesystems generally need Read + Seek; mutation adds Write. Return short reads only when the device genuinely has fewer bytes available, and reject seeks outside the device rather than wrapping arithmetic.

For logical-block-native hardware, implement the traits in hadris-storage and use its seekable block-device adapter. Keep the physical block size and the filesystem's logical sector size distinct.

For memory-backed parsing without std, use hadris_io::Cursor over a caller provided byte slice.